Sunlight Harvesting Transparent Windows

ABSTRACT

A photovoltaic system is formed as a window that is constructed of at least one polymer layer that is filled or decorated with metal nanoparticles and a window frame that includes one or more photovoltaic cells. The metal nanoparticles have a shape and size such that they display surface plasmon resonance frequencies in the near-infrared and/or the near-ultraviolet. The near-infrared and/or the near-ultraviolet radiations are scattered such that they are transmitted parallel to the face of the window to the photovoltaic cells, where an electrical current is generated.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/132,771, filed Mar. 13, 2015, the disclosure of which is herebyincorporated by reference in its entirety, including all figures, tablesand drawings.

BACKGROUND OF INVENTION

A solar panel that allows light to pass through a pane of glass has beena target of scientist for more than a decade as it would permit usingordinary domestic windows to generate electricity with minimumstructural alterations. Such solar cells can be used to harvest sunlightand the artificial light after sundown. One direction that is pursued isto have ultra-thin nearly transparent organic solar cells sprayed asfilms on a pane of glass. These windows are promoted as privacy glass.

Instead of having the entire surface as a light collecting solar cell,some windows are designed to direct the light that hits the entiresurface of the window to the edges of a pane of glass where it iscollected by a solar cell. One approach that has been pursued is byforming a solar concentrating organic coating on a pane of glass thatabsorbs non-visible electromagnetic radiation in sunlight, eitherultraviolet or near-infrared, and re-emit the light at a higherwavelength, infrared, where it is transported across the pane of thewindow to a solar cell at the frame of the window. Alternatively,inorganic nanoparticles, quantum dots, have been co-infused in apolymethylmethacrylate (acrylic) window, where UV, violet and blue lightis absorbed and undergoes a Stokes shift and emits red light thattravels with nearly total internal reflectance to the edge of thewindow.

In another approach inorganic nanoparticle salts have been co-infused ina polycarbonate interlayer, which is then laminated between two platesof ¼″ inch glass to form a window. The nanoparticles scatter componentsof the electromagnetic spectrum to the edge of the glass while lettingmost of the spectrum through. Again, the light that reaches the edge ofthe glass is collected at the window frame by a solar cell imbeddedtherein. The transparent inorganic nanoparticles scatter incomingsunlight with most scattered light traveling laterally in the laminatedstructure to commercial solar cells, such as crystalline silicon cells,at the edges of the glass windows. The window remains highly transparentby proper control of the nanoparticle size and loading in the polymer.Generally, the electrical power generated by such solar windows is quitelow, ˜1 W per square foot. These transparent nanoparticles scattershorter wavelength light effectively, but do not scatter infrared light.Hence, it would be desirable to increase the harvesting of infraredlight without sacrificing the transparency of the windows to the visiblespectrum.

SUMMARY OF THE INVENTION

An embodiment of the invention is directed to a photovoltaic system thatis a window that includes at least one combined nanoparticle polymersheet and a frame that includes at least one photovoltaic cell toreceive at least IR light directed through the window to thephotovoltaic cell for the generation of electricity. The at least onecombined nanoparticle polymer sheet has a transparent polymer that hasat least partial transmittance in at least the visible and near IRregions of the electromagnetic spectrum. The metal nanoparticles can beimbedded within the combined nanoparticle polymer sheet or are decoratedon at least one surface of the combined nanoparticle polymer sheet onsurfaces parallel to the large area faces of the window. The metalnanoparticles are of sizes and shapes that have surface plasmonresonance frequencies in the near-infrared or the near-ultraviolet. Themultiplicity of metal nanoparticles can have a plurality of sizes andshapes and can have a cross-section of 10 to 200 nm. The metalnanoparticles can have a core-shell structure, wherein the core is themetal and the shell is a glass or ceramic. The transparent polymer canbe of one or more polymeric resins or thermoplastics, such as anacrylic, a polycarbonate, or a polyurethane. The window comprises aplurality of combined nanoparticle polymer sheets having a multiplicityof surfaces, where the surfaces are proximal and distal light receivingfaces of the plurality of combined nanoparticle polymer sheets andinterfaces between adjacent combined nanoparticle polymer sheets. Thephotovoltaic cell can be constructed with polycrystalline silicon,monocrystalline silicon, or copper indium gallium selenide. Thephotovoltaic system's window can have one or more glass sheetscontacting combined nanoparticle polymer sheets.

Another embodiment of the invention is directed to preparing thephotovoltaic system. The transparent polymer is combined with themultiplicity of nanoparticles to form at least one combined nanoparticlepolymer sheet in the form of a window. The window is secured into theframe such that at least one edge of the window that is perpendicular toa light receiving face of the window contacts at least one photovoltaiccell situated in the frame such that light directed from the windowperpendicular to the light receiving phase enters the photovoltaic cell.The transparent polymer can be provided as at least one solid curedresin or as a solid thermoplastic as a polymer sheet that is combinedwith the multiplicity of nanoparticles by decorating one or moresurfaces of the polymer sheets. Alternatively, the transparent polymercan be provided as a thermoplastic melt, a polymerizable monomermixture, or an uncured resin and combined with the multiplicity ofnanoparticles by their mixing in a fluid state and solidifying thecombined nanoparticle polymer sheet by cooling a melt, polymerizing amonomer, or curing a resin to lock the nanoparticles within the sheet.One or more glass sheets can be combined with the at least one combinednanoparticle polymer sheet such that glass sheets can protect theplastic and/or act as portions of a wave guide to direct the light intothe photovoltaic cells.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing of a portion of a sunlight harvesting windowaccording to an embodiment of the invention.

FIG. 2 is three light extinction spectra of gold nanoparticles withdifferent sizes. The inset shows a SEM image of a plurality of goldnanoparticles of different shapes that can be dispersed on or withinplastics for the construction of windows, according to embodiments ofthe invention.

FIG. 3 is the light extinction spectra of a set of gold nanoparticleswith a plurality of different shapes nanospheres, nanorods, andnanoprisms, as indicated by the SEM image insets, and sizes that can bedispersed on or within plastics for the construction of windows,according to embodiments of the invention.

FIG. 4 is the light extinction spectra of a set of gold nanorods ofdifferent aspect ratio.

FIG. 5A is a cartoon of the plasmon-driven growth of Au nanoprism.

FIG. 5B illustrates the selective inhibition of facet and subsequentfacet selective growth of Au nanoprism.

FIG. 6A shows the Vis-NIR spectra and TEM images of Au and silicaencapsulated nanospheres.

FIG. 6B shows the Vis-NIR spectra and TEM images of Au and silicaencapsulated nanorods.

FIG. 6C shows the Vis-NIR spectra and TEM images of Au and silicaencapsulated triangular nanoprisms.

DETAILED DISCLOSURE

According to an embodiment of the invention, metal nanocrystals areimbedded into a transparent polymer, such as an acrylic, or decorate thesurface of one or more layers of a transparent polymer, such as apolycarbonate, acrylic, or polyurethane, to selectively scatter certainportions of the solar spectrum from near-ultraviolet to visible tonear-infrared, to a solar cell imbedded in the frame of a window, asillustrated in FIG. 1. The polymer may be in the form of athermoplastic, or in the form of a cured resin. In an embodiment of theinvention, the metal nanoparticles primarily scatter near-infraredand/or near-ultraviolet radiation, although the scattering of a smallportion of the visible light can accompany the scattering of thenear-infrared or near-ultraviolet radiation. The metal nanocrystals canbe a mixture of nanocrystals of different elements or alloys and/or ofdifferent sizes and/or shapes. Due to the mixed composition, a broadportion of the near ultraviolet and/or near-infrared spectrum thatenters the polymer can be directed to the edge and collected at a solarcell situated at the edge of the window at or within the window frame.In this manner, little visible light that would be transmitted throughthe window absent the metal nanoparticles would be lost due to thepresence of the scattering metal nanoparticles. Harvesting of thenear-ultraviolet and/or near-infrared light by the solar cells attachedto the frame perpendicular to the face of the window can increase theelectrical power output of the solar cells as the surface area fromwhich non-visible radiation is scattered is dramatically larger than thesurface of the solar cell, concentrating the radiant energy at the solarcell.

In another embodiment of the invention, the metal nanoparticles mayselectively scatter portions of the visible spectrum in addition tonear-ultraviolet and/or near-infrared light. The use of suchnanoparticles, either by themselves or mixed together with othernanoparticles that primarily scatter near-ultraviolet and/ornear-infrared light, in the same solar window structures can producetinted windows with various colors. Furthermore, an appropriatecombination of multiple types of nanoparticles that produce differentcolor tints can yield color-neutral windows whose visible lighttransmittance can be adjusted by controlling the loading of thenanoparticles in the window structure.

The metal nanoparticles scatter the light at the surface plasmonresonance frequency where excitation of their surface plasmonoscillation occurs. The scattering light intensity is sensitive to thesize and aggregation state of the metal nanoparticles in addition to thecomposition of the metal or alloy. The metals that can be used aresolids, including, but not limited to, noble metals and alloys of noblemetals, such as: ruthenium, rhodium, palladium, silver, osmium, iridium,platinum, gold, rhenium, and copper. The metal nanoparticles can beformed in any manner that provides nanoparticles that are greater thanabout 10 nm but less than about 200 nm. The nanoparticles are of sizesand shapes that display plasmon resonance frequencies in the nearinfrared region or ultraviolet region of the electromagnetic spectrum.As the particles are smaller than the wavelengths of visible light andthe scattered wavelengths are not of the wavelengths of visible light,the windows formed with these nanoparticles display a high lighttransparence and low scattering of visible light. The nanoparticles canbe any shape, for example, as shown in FIG. 2. The nanoparticles can berods or other shapes that do not have equal dimensions but where one ofthe cross-sections is less than 200 nm. In an embodiment of theinvention, the nanoparticles are of a plurality of sizes and shapes toprovide a broad spectrum of near infrared and/or ultraviolet radiationfor absorption by the photovoltaic cells situated in the frame of thewindows.

The plasmon resonant frequency may appear in the visible spectrum by achange in the nanoparticle shape. As shown in FIG. 3, while the goldnanoprisms show primary plasmon resonant frequencies in the infraredregion, the nanorods have primary plasmon resonant frequencies atwavelength range of about 640 nm to 720 nm. Moreover, the nanospheresshow resonant peaks in both the visible (about 530 nm) and infrared(about 800 to 900 nm) regions.

Each type of these nanoparticles can be used to produce a specific tintbecause of their different spectral response. An appropriate combinationof multiple types of nanoparticles can then produce color-neutralwindows that have mostly constant transmittance throughout the visiblespectrum. Certainly, all these visible-scattering nanoparticles can becombined with others that primarily scatter near-infrared and/ornear-ultraviolet light to enhance the overall light harvestingefficiency.

In an embodiment of the invention, the metal nanoparticles are dispersedas filler in a plastic or resin continuous matrix that is a layer thatdefines the surface area of the window. In another embodiment of theinvention, the nanoparticles are dispersed on at least one face of atleast one plastic or resin layer within the window. The window may be ofa laminate structure where a plurality of layers includes at least oneplastic or resin layer. The plastics are advantageous in that theyprovide transparency, structure, impact resistance, and thermalinsulation. The windows can be thicker than a typical single-strengthglass of 3/32″, or double-strength glass of ⅛″, or even plate glass of3/16″. The plastic can be the laminate between multiple layers of glass,for example, the multiple layers of a glass bullet-resistant pane. Theplastic can be a layer of more than one inch in thickness. The polymeris one that does not absorb significantly in the near-infrared, belowabout 1200 nm in wavelength, such as an acrylic resin or a polycarbonatesheet.

The metal nanoparticles are dispersed in the plastic or resin matrixsuch that there are few aggregates of the metal nanoparticles in or onthe polymer layer; for example, the fraction of metal nanoparticles incontact with another metal nanoparticle is 0.1 or less. The metalnanoparticles can be dispersed in a melt or solution, or dispersed in amonomer mixture that includes an initiator upon solidification of themixture. For example, an acrylate resin, which is primarilymethylmethacrylate with other monomers, including cross-linkingmonomers, initiators, and fillers, can be use in a neat liquid phasewhere the metal nanoparticles are dispersed into the monomer mixturewith high-sheer mixing and where the monomer mixture polymerized to thesolid window sheet with little agglomeration of the metal nanoparticlesbefore the mixture is sufficiently viscous to discourage diffusion andagglomeration within the composite. In like fashion a polycarbonate canbe taken up in a solvent and the particles dispersed followed by removalof the solvent, or, alternatively, by the polymerization of meltedcyclic carbonate oligomers with dispersed metal nanoparticles to preparethe polymer layer of the window.

The use of glass sheets, or other low oxygen diffusion sheets, on thefaces of the window, as shown in FIG. 1, permit functioning as a waveguide where internal reflection directs the scattered near-infraredlight through the window perpendicular to the light entry surface to asolar cell within the frame of the window. The window frame contains oneor more solar cells that can collect the scattered near-infrared lightfrom the metal nanoparticles. The solar cells can be any type of solarcell that absorbs sufficiently in the near-infrared, including, but notlimited to: polycrystalline silicon, monocrystalline silicon, or copperindium gallium selenide. In addition to Cu(InGa)Se₂ (CIGS), other directbandgap materials with low gaps can be used for the solar cells in thewindow frames. Other photovoltaic cells, including polymeric and dyesensitized cells, can be designed to extend the absorption of radiantenergy further into the ultraviolet and/or infrared regions of theelectromagnetic spectrum and can be employed in the window basedphotovoltaic system. The exterior faces of the window can be a polymerof like or dissimilar composition as the polymer with the decorated orinfused metal nanoparticles. The frame can be constructed of a pluralityof solar cells combined as an array.

In embodiments of the invention, windows with high visible lighttransmission (VLT) contain only IR-scattering nanoparticles. In otherembodiments of the invention, photovoltaic windows having blue, green,or brown hues are formed by inclusion of visible and IR scatteringnanoparticles into the films on the windows. These windows can includepigments and other components that additionally or exclusively providethe colors of the tinted windows. In another embodiment of theinvention, multiple types of visible-scattering nanoparticles can becombined to achieve low VLT/non-tinted photovoltaic windows or low VLTtinted windows with the additional inclusion of pigments.

Efficient scattering of visible and NIR light is required to achievesolar windows where the VLT ranges from low to high. Thelight-harvesting nanoparticles included in the window must be capable ofscattering across a broad range of the solar spectrum. The surfaceplasmon resonance (SPR) of plasmonic metal NPs can be tuned to maximizethe scattering of incident light over a broad range by manipulatingtheir sizes and shapes. Selective use of nanorods or nanoprisms allowsalteration of the SPR modes of the nanoparticles across the entirevisible and NIR regions of the solar spectrum, as shown in FIG. 3.Plasmonic nanospheres (˜400-550 nm), nanorods (˜500-900 nm), andnanoprisms (˜800-1400 nm) can be used to promote scattering across thebroad range of 400 to 1400 nm. It is also noted that thosesolution-based methods employed herein can be easily extended forlarge-scale nanomaterials synthesis. In embodiments of the invention, Aunanoparticle of differing morphologies can be used, according toembodiments of the invention. Small Au seed nanoparticles (d≈4-6 nm) canbe prepared by NaBH₄ reduction of HAuCl₄, and can be used for subsequentgrowth in aqueous solution. Such aqueous solutions contain cappingagents, including, but not limited to, cetyltrimethylammonium bromide(CTABr)), and HAuCl₄·3H₂O, and reducing agents, such as, but not limitedto, ascorbic acid, with base solution employed to adjust pH. By varyingsolution temperature, pH, and HAuCl₄ concentration, various Aunanoparticles can be produced.

In other embodiments of the invention, the optical properties of thecolloids can be tuned by the use of plasmonic alloys, such as, but notlimited to, Au/Ag alloy or by use of core-shell nanoparticles, such as,but not limited to, Au-Ag core-shell nanoparticles. Such particles canbe formed by the simultaneous or sequential reduction of, for example,HAuCl₄ and AgNO₃ salts. The LSPR of Au nanoprisms occurs around 1200 nm,but formation of a glass shells on a Au nanoprism induces a significantblue-shift in the LSPR maximum to about 1000 nm.

In an embodiment of the invention, Au nanorods can be used as “seeds”for the subsequent growth of anisotropic Au nanorods and/or nanowires.The length of the Au nanorods can be tuned by changing the concentrationof the capping reagent, such as CTABr, and the ratio of the Au seeds tothe HAuCl₄ precursors in the growth solution. The plasmon bands of theAu nanorods can be chosen from ˜550-900 nm and can be combined to extendthe absorption across any portion of the visible and near-IR spectrum,as shown in FIG. 4. Interestingly, our initial results revealed that theAu nanoparticle morphology can be easily tuned by simply varying theiodide (I) concentration in the growth solution. Bu controlling theamount of iodide in the solution, a large population of nanorods can beobtained when no I⁻ is in solution or a large population of nanoprismsat concentration of I⁻ greater than 10 with the shapes and scatteringshown in FIG. 2. By further adjusting the I⁻ concentration, tiptruncation of the nanoprisms can be controlled to alter the LSPRproperties. For instance, the LSPR of the nanoprisms can be tuned from1000-1200 nm by changing the I concentration from 50-500 μM NaI in thegrowth solution. The nanorod or nanoprism aspect ratio can be tuned byadjusting the ratio of seed particles to metal precursors in the growthsolution.

Light-mediated synthesis of metal nanocrystals allows synthesis ofnanostructures with precise control over morphology. In this manner, Agnanoprisms have been prepared that have strong absorption in the NIRregion, where the architecture of the nanoprisms correlates in aquasi-linear fashion with the in-plane dipole plasmon band. When thelight has a wavelength that matches the SPR bands of the plasmonic seednanoparticles in the solution, nanoparticle growth is initiated. The SPRbands of the growing nanoparticles red-shifts as their sizes and shapeschange. Once the SPR bands shift from that of the light source,nanoparticle growth stops. By adjustment of the illumination to matchthe new SPR bands, growth of the nanoparticle can be continued in acontrolled manner. By this method, Au nanoprisms with strong SPRabsorption in the NIR region can be prepared. Using sharp band-passfilters for narrow wavelength distribution or by use of lasers as thelight source, Ag nanoparticles with uniform size and shape can beacquired in high yield.

Pseudo-spherical Au nanoparticles with an average size of ca. 7±3 nm areuseful as seeds for plasmon-driven growth of anisotropic Au nanoprisms.Photochemical growth solution can be prepared by addingpolyvinylpyrrolidone (PVP) to pure H₂O and methanol to which HAuCl₄aqueous solution and Au seed solution are added and gently mixed. Asillustrated in FIG. 5A, for high yield synthesis of Au nanoprism, growthsolution is first incubated in the dark to preferentially enlargemultiply-twinned seeds while rendering planar-twinned seeds relativelyunreactive in the dark. The multiply-twinned nanoparticles are largeenough (d>100 nm) to be readily separated from the planar-twinned seeds(d˜15 nm) by centrifugation. The supernatant of highly enriched withplanar-twinned nanocrystals is irradiated at an incident power I₀ ofabout 12 mW/cm² to produce Au nanoprisms in high yield. The facets alongthe nanoprism perimeter is alternatively enclosed by { 111 } and {100}facets. If a facet-selective species such as iodide is in the growthsolution, preferential passivation of { 111 } facets occurs with growthoccurring on the {100} facets to yield triangular nanoprisms as thedominant photoproducts, as indicated in FIG. 5B.

The optical properties of plasmonic nanoparticles are highly sensitiveto their physical morphology and, therefore, it is essential to preservethe geometry of the nanoparticles to ensure consistent operation overtime. In an embodiment of the invention, glass or ceramic shells, forexample, silica (SiO₂) shells, coat plasmonic metal nanoparticles (Au,Ag, etc.). These core-shell nanoparticles are used to provide plasmonicmaterial with enhanced chemical stability due to the silica physicalbarrier between the metal and its environment. After the desirednanoparticles are synthesized, coating with SiO₂ shells results byinjecting small quantities of tetraethoxysilane (TEOS) to form silica onthe nanoparticles source. By adjusting the amount of TEOS and the numberof its additions to the growth solution, the thickness of the SiO₂ shellcan be tuned from about 5 to 25 nm. These conformal coatings preservethe optical response of the metal nanoparticle colloid, as illustratedfor various morphologies of Au and Au-silica core-shell nanoparticles inFIG. 6A, 6B and 6C. In addition to SiO₂, the glass or ceramic shell canbe another metal oxide, including, but not limited to TiO₂, Al₂O₃, SnO,Al₂O₃, B₂O₃, ZrO₂, SnO₂, any combination thereof, or any other metaloxide.

In the first method, the properly functionalized nanoparticles may bemixed with the PMMA monomers. The organic-inorganic composite materialwill then be spread out on a glass plate followed by the pressing of thesecond plate on top. For commercial production, it is conceivable toinjection mold the PMMA/metal nanoparticle composite material into thinsheets, which are then laminated between two glass plates to produce thedesired waveguide. This mixing method can easily adjust the loading ofthe nanoparticles, and with variable PMMA layer thickness, the amount ofnanoparticles within the waveguide and therefore the opticaltransmittance can be readily tuned. However, it may be difficult tocontrol the orientation of the anisotropic particles, which could provecritical for achieving high solar conversion efficiencies in thephotovoltaic windows.

To control orientation of the anisotropic nanoparticle, such asnanoprisms and nanoplates, direct deposition onto one glass plate usingsolution processes such as spin coating or spray coating can be carriedout. If desired or required, glass surface may need to be pretreated inoxygen plasma to improve wetting of the nanoparticle containing solutionon the surface. For Example, Norland Optical Adhesive (NOA) precursorscan be spread on a second glass plate, which is then pressed against thenanoparticle-coated surface of the first glass plate. The waveguide iscompleted by curing the NOA under UV irradiation. Multiple coatings ofthe nanoparticles can be formed, for example, by depositing a layer ofnanoparticles on the first glass plate, spraying dissolved NOA, forexample in toluene, onto the nanoparticles and rapidly drying andUV-polymerizing the NOA. Subsequently, repeated depositions ofadditional nanoparticles and polymerized NOA layers allow a host ofnon-aggregable metal nanoparticles. The number of coating cycles and theconcentration and solution deposition conditions can be varied tocontrol the amount of the plasmonic nanoparticles within the waveguide.Photovoltaic windows are constructed by attaching commercially availablesolar cells to the edges of the waveguide using optical adhesives.

It should be understood that the embodiments described herein are forillustrative purposes only and that various modifications or changes inlight thereof will be suggested to persons skilled in the art and are tobe included within the spirit and purview of this application.

We claim:
 1. A photovoltaic system, comprising a window and a framecomprising at least one photovoltaic cell, wherein the window comprisesat least one combined nanoparticle polymer sheet comprising atransparent polymer and a multiplicity of metal nanoparticles, andwherein the photovoltaic cell resides in the frame perpendicular to alight receiving face of the window, and wherein the transparent polymerhas at least partial transmittance in at least the visible and near IRregions of the electromagnetic spectrum.
 2. The photovoltaic systemaccording to claim 1, wherein the metal nanoparticles are imbedded inthe combined nanoparticle polymer sheet.
 3. The photovoltaic systemaccording to claim 1, wherein the metal nanoparticles decorate on leastone surface of the combined nanoparticle polymer sheet on a planeparallel to the large area faces of the window.
 4. The photovoltaicsystem according to claim 1, wherein the majority of the metalnanoparticles are isolated from each other, and wherein the fraction ofmetal nanoparticles in intimate contact is 0.1 or less.
 5. Thephotovoltaic system according to claim 1, wherein the metalnanoparticles are of sizes and shapes that have surface plasmonresonance frequencies in the near-infrared or the near-ultraviolet. 6.The photovoltaic system according to claim 1, wherein the multiplicityof metal nanoparticles are of a plurality of sizes and shapes.
 7. Thephotovoltaic system according to claim 1, wherein the multiplicity ofmetal nanoparticles have a cross-section of 10 to 200 nm.
 8. Thephotovoltaic system according to claim 1, wherein the metalnanoparticles comprise a metal selected from ruthenium, rhodium,palladium, silver, osmium, iridium, platinum, gold, rhenium, and copper,and alloys thereof.
 9. The photovoltaic system according to claim 8,wherein the metal nanoparticles comprise a core-shell structure, andwherein the core comprises the metal and the shell is a glass orceramic.
 10. The photovoltaic system according to claim 9, wherein theglass or ceramic comprises, SiO₂, TiO₂, Al₂O₃, SnO₂, ZrO₂, or anycombination thereof.
 11. The photovoltaic system according to claim 1,wherein the transparent polymer comprises one or more polymeric resinsor thermoplastics.
 12. The photovoltaic system according to claim 11,wherein the polymeric resin or thermoplastic comprises an acrylic, apolycarbonate, or a polyurethane.
 13. The photovoltaic system accordingto claim 1, wherein the window comprises a plurality of combinednanoparticle polymer sheets having a multiplicity of surfaces whereinthe surfaces are proximal and distal light receiving faces of theplurality of combined nanoparticle polymer sheet and interfaces betweenadjacent combined nanoparticle polymer sheets.
 14. The photovoltaicsystem according to claim 1, wherein the photovoltaic cell comprisespolycrystalline silicon, monocrystalline silicon, or copper indiumgallium selenide.
 15. The photovoltaic system according to claim 1,wherein the multiplicity of metal nanoparticles are spheres, rods,prisms, disks, rice-shaped, shelled, donut-shaped, or any combinationthereof.
 16. The photovoltaic system according to claim 1, wherein themultiplicity of metal nanoparticles imparts a tint, a color-neutrality,or a variable light transmittance over portions of the window.
 17. Thephotovoltaic system according to claim 1, wherein the combinednanoparticle polymer sheet contacts and resides against at least oneglass sheet.
 18. A method of preparing a photovoltaic system accordingto claim 1, comprising: providing a transparent polymer; combining thetransparent polymer with a multiplicity of nanoparticles to form atleast one combined nanoparticle polymer sheet that comprises a window;placing the window into a frame comprising at least one photovoltaiccell situated against at least a portion of at least an edge of theframe and contacting the window on an edge perpendicular to a lightreceiving face of the window; and securing the window within the frame.19. The method of claim 18, wherein the transparent polymer is providedas at least one cured resin or as a thermoplastic in a solid state as atleast one polymer sheet combining with the multiplicity of nanoparticlescomprises decorating one or more surfaces of the at least one polymersheets.
 20. The method of claim 18, wherein the transparent polymer isprovided as a thermoplastic melt, a polymerizable monomer mixture, or anuncured resin; wherein combining comprises mixing the transparentpolymer in a fluid state with the multiplicity of nanoparticles andsolidifying to form a combined nanoparticle polymer sheet.
 21. Themethod of claim 18, further comprising: providing at least one sheet ofglass; and attaching the at least one combined nanoparticle polymersheet to the at least one sheet of glass, wherein the window furthercomprises the at least one sheet of glass.